vapour pressure deficit
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2022 ◽  
Author(s):  
Shijie Li ◽  
Guojie Wang ◽  
Chenxia Zhu ◽  
Jiao Lu ◽  
Waheed Ullah ◽  
...  

Abstract. Actual evapotranspiration (ET) is an essential variable in the hydrological process, linking the carbon, water, and energy cycles. Global ET has significantly changed in the warming climate. Although increasing vapour pressure deficit (VPD) due to global warming enhances atmospheric water demand, it remains unclear how the dynamics of ET are affected. In this study, using multiple datasets, we disentangled the relative contributions of precipitation, net radiation, air temperature (T1), VPD, and wind speed on affecting annual ET linear trend using an advanced separation method that considers the Budyko framework. It is found that the precipitation variability dominantly controls global ET in the dry climates, the net radiation has substantial control over ET in the tropical regions, and VPD is impacting ET trends in boreal mid-latitude climate. The critical role of VPD in controlling ET trends is particularly emphasized due to its influence in controlling the land-atmosphere interactions.


Agronomy ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 52
Author(s):  
Xi Sun ◽  
Jie Li ◽  
Donald Cameron ◽  
Gregory Moore

The measurement of sap movement in xylem sapwood tissue using heat pulse velocity sap flow instruments has been commonly used to estimate plant transpiration. In this study, sap flow sensors (SFM1) based on the heat ratio method (HRM) were used to assess the sap flow performance of three different tree species located in the eastern suburbs of Melbourne, Australia over a 12-month period. A soil moisture budget profile featuring potential evapotranspiration and precipitation was developed to indicate soil moisture balance while the soil-plant-atmosphere continuum was established at the study site using data obtained from different monitoring instruments. The comparison of sap flow volume for the three species clearly showed that the water demand of Corymbia maculata was the highest when compared to Melaleuca styphelioides and Lophostemon confertus and the daily sap flow volume on the north side of the tree on average was 63% greater than that of the south side. By analysing the optimal temperature and vapour pressure deficit (VPD) for transpiration for all sampled trees, it was concluded that the Melaleuca styphelioides could better cope with hotter and drier weather conditions.


2021 ◽  
Author(s):  
Hartmut Kaiser ◽  
Amit Sagervanshi ◽  
Karl H. Mühling

Abstract Background Leaf hydration is controlled by feedback mechanisms, e.g. stomatal responses, adjustments of osmotic potential and hydraulic conductivity. Leaf water content thus is an input into related feedback-loops controlling the balance of water uptake and loss. Apoplastic alkalisation upon leaf dehydration is hypothesized to be involved in water stress related signaling on tissue level. When studying these mechanisms and their intermediate signaling steps, an experimenter has only poor means to actually control the central experimental variable, leaf water content (LWC), because it is not only dependent on external variables (e.g. air humidity), which are under experimental control, but is also governed by the biological influences controlling transpiration and water uptake. Those are often unknown in their magnitude, unpredictable and fluctuating throughout an experiment and will prevent true repetitions of an experiment. The goal of the method presented here is to experimentally control and manipulate leaf water content (LWC) of attached intact leaves enclosed in a cuvette. Results An experimental setup was developed where LWC is measured by a sensor based on IR-transmission and its signal processed to control a pump which circulates air from the cuvette through a cold trap. Hereby a feedback-loop is formed, which by adjusting vapour pressure deficit (VPD) and consequently leaf transpiration can precisely control LWC. This technique is demonstrated here in a combination with microscopic fluorescence imaging of apoplastic pH (pH apo ) as indicated by the excitation ratio of the pH sensitive dye OregonGreen. Initial results indicate that pH apo of the adaxial epidermis of Vicia faba is linearly related to reductions in LWC. Conclusions Using this setup, constant LWC levels, step changes or ramps can be experimentally applied while simultaneously measuring physiological responses. The example experiments demonstrate that bringing LWC under experimental control in this way allows better controlled and more repeatable experiments to probe quantitative relationships between LWC and signaling and regulatory processes.


Food Research ◽  
2021 ◽  
Vol 5 (6) ◽  
pp. 109-118
Author(s):  
D. Lentzou ◽  
G. Xanthopoulos ◽  
C. Templalexis ◽  
A. Kaltsa

Transpiration and respiration are two mechanisms of water loss in fresh agricultural products, resulting in visual and texture degradation. Neglecting respiration as a mechanism of water loss may lead to erroneous results at saturation where water vapour pressure deficit is zero and thus water loss is expected to be zero, however, the existence of a finite water loss is noted. In this context, an analysis of the associated with transpiration and respiration water loss in figs (Ficus carica L.) was carried out at 0oC, 10oC and 20oC and 45.64%, 80.22% and 98.65% relative humidity as well as the air conditions of walk-in cold storage rooms. The estimated transpiration rate ranged between 0.11-1.416 mg cm-2 h -1 for a water vapour pressure deficit of 0.0-0.98 kPa. The water vapour pressure deficit estimation was based on the difference between cold air temperature and figs’ surface temperature. The respiration rate was calculated at 0oC, 10oC and 20oC as 0.47±0.08, 0.94±0.11 and 2.69±0.17 mLCO2100g-1 h -1 . Quantification of the water loss showed that at 20oC and saturation, the water loss due to respiration accounts for 3.9% of the respective water loss due to water vapour pressure deficit while on average, the water loss due to respiration accounts for 1.5%, 2.1% and 2.6% of the water loss due to water vapour pressure deficit at 0oC, 10oC and 20oC.


2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Katrina J. BROUGHTON ◽  
Paxton PAYTON ◽  
Daniel K. Y. TAN ◽  
David T. TISSUE ◽  
Michael P. BANGE

Abstract Background Plants respond to changes in vapour pressure deficit (VPD) between the leaf and the atmosphere through changes in stomatal response, which can consequently affect transpiration, photosynthesis, and leaf-level water use efficiencies. With projected warmer air temperatures, changes in rainfall distribution and altered VPD in future climates, it is important to understand the potential effect of VPD on leaf-level physiology of field-grown crops. The aim of this study was to assess the impact of altered VPD on leaf-level physiology of field-grown cotton to improve the current understanding of the plant-by-environment interaction, thereby contributing to validation and improvement of physiological and yield response models. Different VPD environments in the field were generated by planting cotton on three dates within the sowing window (early-season (S1) = 5th October 2011; mid-season (S2) = 9th November 2011; and late-season (S3) = 30th November 2011). VPD was also modified by altering crop irrigations. Results VPDL accounted for the largest proportion of the explained variation in both stomatal conductance (32%∼39%) and photosynthetic (16%∼29%) responses of cotton. Generally, smaller percentages of variation were attributed to other main factors such as the individual plant (Plant), and accumulated temperature stress hours (ASH; a measure of plant water status over time) and interactive factors, including leaf vapour pressure deficit (VPDL) × Plant and Plant × ASH; however, a proportion of variation was unexplained. In addition, the Asat/E (instantaneous transpiration efficiency, ITE) model developed based on cotton grown in the glasshouse was applied to cotton grown in the field. We found that the modelled Asat/E and field-measured Asat/E were very similar, suggesting that the mechanistic basis for ITE was similar in both environments. Conclusions This study highlights the importance of accounting for VPD in climate change research, given that stomata are highly responsive to changes in VPD. This experiment provides a basis for physiology and production models, particularly in terms of cotton response to projected climatic environments.


2021 ◽  
Vol 23 (4) ◽  
pp. 381-388
Author(s):  
MAHESH CHAND SINGH ◽  
J. P. SINGH ◽  
K. G. SINGH ◽  
O. P. GUPTA ◽  
G. KUMAR

The plant water or nutrient requirement under greenhouse conditions is mainly governed by crop transpiration in a linear relation to vapour pressure deficit (VPD), particularly in soilless production systems. Being a cooling process in plants, transpiration governs the plant water requirement in relation to the subjected microclimatic conditions and VPD can be used as a tool to maintain greenhouse crop transpiration to optimal range for obtaining desired crop yields. Thus, the present investigation was undertaken to study the integrated effect of temperature (Tapc), relative humidity (Eapc) and solar radiation (Irad) on VPD and crop transpiration. A computer module was developed to monitor the behavior of the VPD and thereby the crop transpiration through charts under greenhouse conditions. The VPD indicated a linear increasing trend with Tapc (R2≥0.84) and decreasing trend with Eapc (R2=0.99), demonstrating a strong correlation in both cases. The increasing crop transpiration with VPD, particularly under hot climatic conditions significantly increased the input water and nutrient requirements of the crop. Thus, transpiration in relation to VPD should be considered as a factor for fertigation scheduling and improving irrigation control in soilless systems. Moreover, maintaining Tapc, Eapc and VPD within range of 22-27°C, 60-80% and 0.53-1.10 kPa may help to control the crop transpiration, manage the greenhouse irrigation and fertigation, and thus improve the cucumber yield.


2021 ◽  
Vol 12 ◽  
Author(s):  
Dalong Zhang ◽  
Qingjie Du ◽  
Po Sun ◽  
Jie Lou ◽  
Xiaotian Li ◽  
...  

The atmospheric vapour pressure deficit (VPD) has been demonstrated to be a significant environmental factor inducing plant water stress and affecting plant photosynthetic productivity. Despite this, the rate-limiting step for photosynthesis under varying VPD is still unclear. In the present study, tomato plants were cultivated under two contrasting VPD levels: high VPD (3–5 kPa) and low VPD (0.5–1.5 kPa). The effect of long-term acclimation on the short-term rapid VPD response was examined across VPD ranging from 0.5 to 4.5 kPa. Quantitative photosynthetic limitation analysis across the VPD range was performed by combining gas exchange and chlorophyll fluorescence. The potential role of abscisic acid (ABA) in mediating photosynthetic carbon dioxide (CO2) uptake across a series of VPD was evaluated by physiological and transcriptomic analyses. The rate-limiting step for photosynthetic CO2 utilisation varied with VPD elevation in tomato plants. Under low VPD conditions, stomatal and mesophyll conductance was sufficiently high for CO2 transport. With VPD elevation, plant water stress was gradually pronounced and triggered rapid ABA biosynthesis. The contribution of stomatal and mesophyll limitation to photosynthesis gradually increased with an increase in the VPD. Consequently, the low CO2 availability inside chloroplasts substantially constrained photosynthesis under high VPD conditions. The foliar ABA content was negatively correlated with stomatal and mesophyll conductance for CO2 diffusion. Transcriptomic and physiological analyses revealed that ABA was potentially involved in mediating water transport and photosynthetic CO2 uptake in response to VPD variation. The present study provided new insights into the underlying mechanism of photosynthetic depression under high VPD stress.


2021 ◽  
Author(s):  
Victor Flo ◽  
Jordi Martínez-Vilalta ◽  
Víctor Granda ◽  
Maurizio Mencuccini ◽  
Rafael Poyatos

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